The present invention relates to a system designed so that the distance from an automotive vehicle to an obstacle in the rear of the vehicle is detected and indicated by means of ultrasonic waves, thus aiding the driving of the vehicle during its backward movement.
In the past, both systems employing ultrasonic waves and systems employing optical instruments for the purpose of detecting an obstacle in the rear of a vehicle have been proposed. These systems have been necessarily mounted on the exterior trimming of the vehicle compartment and consequently the systems have been placed in surroundings where they are subject to temperature and humidity as well the deposition of dirt or dust. In particular, the deposition of dirt or dust has considerably deteriorated the functions of these systems. Thus, these systems have been subject to the trouble of requiring frequent and positive checks despite the systems being mounted on the exterior trimming at the rear part of the vehicle compartment where it is very difficult to look at. The addition of a self-checking device for overcoming this difficulty results in a considerable increase in the cost.